Subscriber s equipment for program transmission



Dec. 29,1925- 1,567,209

J. F. TOOMEY SUBSCRIBERS EQUIPMENT FOR PROGRAM TRANSIIISSION FiledDec. 1. 1923 '&w a& aim l umw -Janmw 129mm m.hwJ J IN VEN TOR PatentedDec. 29, 1925.

UNITED STATES PATENT OFFICE.

JOHN F. TOOMEY, OF NEN YORK, N. Y., ASSIGNOR T0 AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SUBSGRIBERS EQUIPMENT FOR PROGRAM TRANSMISSION.

Application filed December 1, 1923. Serial No. 677,992.

To all whom it may concern:

Be it known that 1, JOHN F. TOOMEY, residing at New York, in the countyof New York and State of New York, have invented certain Improvements inSubscribers Equipment for Program Transmlssion, of which the followingis a specification.

This invention relates to program trans mission over wires andparticularly'to systems in which a program channel, employing audiofrequencies, is superposed upon an ordinary subscribers telephone line.

It has been proposed to use ordinary subscribers telephone lines forprogram purposes by transmitting program currents over the lines atvoice frequencles dur ng such times as the telephone line is not belngused for ordinary telephonic purposes. Under such circumstances, it isdesirable that the program system be so superposed on the telephone linethat the program apparatus will be disconnected either when a call comesin to the subscribers line or when the sub scriber desires to send out acall.

It is one of the objects of the present invention to so arrange thesubscribers apparatus that a low impedance loud speaker may be used atthe subscribers station for program purposes and may be disconnected 0automatically as soon as the operator plugs into the subscribers line.The disconnection actually takes place before the l1ne 1s disconnectedfrom the program equipment at the central office and connected to thecalling jacks. This is a particularly desirable feature where machineringing 1s employed, as the ringing current flowing through the lowimpedance loudspeaker might trip the machine ringing apparatus if the.loud speaker were not disconnected. Another object of the invention isto so arrange the subscribers circuit that the loud speaker will bedisconnected at once upon taking the receiver from the switchhook of thetelephone set. Other and further objects of the invention will appearmore fully hereinafter; I

The invention may now be understood from the following description whenread in connection with the accompanying drawings, Figures 1, 2 and 3 ofwhich illustrate different modifications of the invention.

Referring to Fig. 1, L designates an ordinary telephone subscribers lineterminating at the subscribers substation in the usual substation set10. At the central oflice the subscrlbers line is connected over thecontacts of the cut-off relay CO to the primary of a transformer 11, thesecondary of which is 111 circuit with a trunk T leading to a programstation. The line relay LR is connected 1n circuit with the primarywinding of the transformer 11, as shown, and the usual line lamp 12 iscontrolled by the line relay. The cut-off relay CO is so arranged thatwhen operated in response to the insertlon of a plug in jacks such as Jand J the line L will be disconnected from the program circuit andconnected to the switchmg jacks.

At the subscribers station the loud speaker 13 is arranged to be bridgedacross the subscribers line L over a contact of the swltchhook 14: andover a contact controlled by a high resistance relay R. The relay R isalso bridged across the subscribers line upon the actuation of thecontact 15 of a nonlocklng key K, the relay R being locked up when onceactuated and thereby maintaining the loud speaker in connection with thesubscribers line. The circuit of the high resistance relay R is arrangedso that it will be opened immediately upon inserting a plug in a callingjack at the central office and before the cut-off relay has had time tooperate and connect the subscribers line to the calling jacks. The highresistance relay is therefore immediately unlocked and'deenergized toopen the loud speaker circuit. The relay R will also be unlocked in asimilar manner by taking the receiver ed the switchhook to initiate atelephone call at the subscribers station or by actuating the contact 16of the non-locking key at the end of the transmission of the program.

The operation is as follows: If the subscriber desires to receiveprogram trans mission he momentarily actuates the nonlocking key toclose the contact 15. This completes a circuit for the high resistancerelay It from battery at the central oiiice over the back contact of therelay S, through the right-hand winding of the line relay LR, over thelower back contact of cut-ofi relay CO, ring side of the line L, overswitchhook contact 1 1, normally closed contact 16 of key K, momentarilyclosed contact 15 of key K, through the winding of the relay R, over thetip side of the line L, upper back contact of cut-01f relay CO andthrough the IOU right-hand winding of the line relay LR to ground. Therelay R is actuated over the circuit above traced but the resistance ofsaid relay is so high that it does not permlt the line relay LR to beactuated. The relay R- is locked up over its inner front contactindependently of the contact 15, wh1ch is opened as soon as the key K isreleased. At its outer front contact relay R closes a bridge circuit 17through the loud speaker 13 and over the contact 14: of the switchhook.

In order to prevent the low impedance loud speaker 1.3 from actuatingthe line relafy LR, a condenser 18 is inserted in series therewith. Thesubscribers line is normally connected over the back contact of thecut-off relay CO and through the transformer 11 to the trunk T leadingto the program source and consequently the circuit is now in conditionto receive the program transmission.

If, while the line is being used for program purposes, a call comes infor the subscribers station the operator inserts a plug in one of themultiple jacks J or J, thereby closing a circuit over the sleeve of thejack for the relay S. The relay S, upon being energized, attracts itsarmature and disconnects battery from the ring side of the line L sothat the relay R is at once released and unlocked, at the same timeopening the circuit of the loud speaker 13. The relay S, at its frontcontact, closes a circuit for the cutoff relay CO, which disconnects theline L from the trunk T and connects it to'conducto'rs leading to themultiple jacks J and J. Battery is now supplied over the ring side ofthe line through the cord circuit but as the relay R has been unlockedit will not be again actuated 'since the contact 15 of the non-lockingkey K is open.-

It will be seen that the relay R is released to open the circuit of loudspeaker '13 before the line L is actually connected to the answeringjacks and consequently there is no possibility that ringing current willpass through the loud speaker 13.

In case the subscriber should desire to initiate a call while the lineis being used for program receiving he merely takes the receiver off theswitchhook, thereby opening the contact 14, which causes the relay R tobe released and unlocked, thus opening the circuit 17 through the loudspeaker 13. The line relay LR Will be operated through the lowresistance path of the subscribers set 10 and will cause the line lamp12 to glow. The operator, in response to the line lamp, inserts ananswering plug in one of the jacks J or J, with results alreadydescribed.

When the subscriber is receiving program transmission and desires to bedisconnected from the program station he simply presses the non-lockingkey K to momentarily open the contact 16, thereby releasing the relay Rand unlocking the same. The relay R in turn opens the circuit of theloud speaker 13 so that the program transmission can no longer be heard.

A modification is shown in Fig. 2, in which the loud speaker circuitincludes an amplifier. The amplifier comprises a vacuum tube 19 of theusual type, having its plate circuit connected through a trans former 20to the loud speaker 19. Its grid circuit is connected through atransformer 21 to the bridge circuit 17 of the subscriber's set. Inorder to provide operating currents for the amplifier, a transformer isprovided having a primary winding 22 connected to suitable A. G. powermains and having secondary windings 23, 21 and 25. The secondary windingsteps down the voltage to a value such, for example, as six volts,suitable for operating the filament of the amplifier 19. The secondarywinding 21:, on the other hand, steps the voltage to a value such, forexample, as 110 volts. suitable for supplying the plate current of theamplifier 19.

In order to rectify the plate current a vacuum tube rectifier 26 isprovided. The grid and plate of this tube may be connected together toform the positive electrode while the filament, as usual, constitutesthe negative electrode. The discharge path of the tube is connected inseries between the secondary 24 and .the plate of the tube 19. Thefilament of the tube 29 is supplied with current through the secondary25. which'steps'down the voltage to a. value such, for example, as sixvolts, suitable for the filament supply.

In order to smooth out the rectified current supplied to the plate ofthe tube 19 a choke coil 27 is included in series with the plate and, ifdesired, a condenser 28. may be shunted across the plate circuit toby-pass the high frequency components. In order to eliminate, so far aspossible, the noise of the A. G. current supplied to the filament of thetube 19, the plate of said tube is connected through a condenser 29 andthe resistance 30 to the midpoint of the secondary 23.

The circuit arrangement of the remainder of the subscribers set and thecircuits at the central ofiice are the same as those de scribed inconnection with Fig. 1, and the operation is also the same, the onlydifference being that the amplifier 19 amplifies the programtransmission received in the circuit 17 before impressing it upon theloud speaker 13. The operation of the amplifying equipment will beobvious from the description already given and it will be understoodthat when the program equipment is not in use the leads from theamplifier to the power mains will be opened by a suitable switch.

Fig. 3 illustrates a similar arrangement differing from that of Fig. 2only in that the amplifier is supplied from direct current power mains.As in the case of the amplitier of Fig. 2, the amplifier in Fig. 3consists of a vacuum tube 19, having its output circuit connectedthrough a transformer 20 to a loud speaker 13 and its grid circuit connected through a transformer 21 to the bridge circuit 17. In this case,however, the connection to the bridge circuit is made through apotentiometer 31 of well known construction. The grid or C battery maybe supplied from dry cells and the same holds true for the platecurrent. The filament current, however, is supplied from direct currentpower mains through a resistance 32. The remaining apparatus, both atthe central oflice and at the substation, is similar to that of Fig. 1and operates in the same manner. As the operation of the amplifier isobvious no description of the circuit operation is necessary.

It will be obvious that the general principles herein disclosed may beembodied in many other organizations widely different from thoseillustrated without departing from the spirit of the invention asdefined in the following claims.

\Vhat is claimed is:

1. In a program system, a telephone line having switching terminals,means to connect said telephone line to a program station, programreceiving equipment associated with said telephone line, meanscontrolled by a subscriber for connecting said receiving equipment tothe line and means responsive to the establishment of a telephoneconnection to the switching terminals of the line for automaticallydisconnecting said receiving equipment and thereafter connecting theline to the switching terminals.

2. In a program system, a subscribers telephone line, means forconnecting said line to a program station, program receiving equipmentassociated with said line, means including a relay that can be operatedunder the control of the subscriber for c011- necting said receivingequipment to the line, switching terminals for the line, and meansresponsive to the establishment of a connection to said switchingterminals for releasing said relay to disconnect the receiving equipmentand for thereafter connecting the line to the switching terminals.

3. In a program system, a subscribers telephone line, connections fromsaid line to a program station, program receiving equipment associatedwith said line, a relay for connecting said receiving equipment to theline, means controlled by the subscriber for operating and locking upsaid relay, switching terminals for the line, and means responsive tothe establishment of a connection to said switching terminals formomentarily disconnecting battery from the line, thereby releasing andunlocking said relay, and means for thereafter connecting the line tothe switching terminals.

i. In a program system, a subscribers telephone line, a. cut-off relay,means for connecting said line over the contacts of said cut-off relayto a program station, program receiving equipment adapted to be bridgedacross the subscribefis line, a relay for establishing said bridge,means under the control of the subscriber for establishing a circuitthrough said last mentioned relay over the line conductors to a sourceof current at the central office, Witching terminals for said line atthe central office, means responsive to the establishment of aconnection to said switching terminals for disconnecting said currentsource from the line to release said last mentioned relay and disconnectsaid program receiver, and means for thereafter actuating the cut-offrelay to establish a connection from the line to said switchingterminals.

5. In a program system, a subscribers telephone line, means to connectsaid subscribers line to a program station, program receiving equipmentadapted to be bridged across said line, said equipment including a loudspeaking receiver and an amplifier, means to bridge said equipmentacross the subscribers line under the control of the subscriber,switching terminals for said line, and means responsive to theestablishment of a connection to said switching terminals for openingthe connection to said receiving equipment and thereafter connecting theline to said switching terminals.

In testimony whereof, I have signed my name to this specification this30th day of November, 1923.

JOHN F. TOOMEY.

